元素分析-稳定同位素质谱法结合化学计量学鉴别橄榄油掺假

为建立快速鉴别橄榄油掺假的检测方法,以特级初榨橄榄油、玉米油、猪油、牛油和鸭油为实验材料,通过元素分析-稳定同位素质谱仪测定油脂的δ¹³C、δ¹⁸O和δ²H,并结合化学计量学鉴定橄榄油掺假。采用主成分分析(PCA)和正交偏最小二乘法判别分析(OPLS-DA)两种统计分析方法建立不同油脂的鉴别模型和橄榄油掺假鉴别模型。结果表明：橄榄油的δ¹³C、δ¹⁸O和δ²H范围分别在-30.411×10^-3～-28.996×10^-3、23.583×10^-3～25.581×10^-3、-163.611×10^-3～-132.251×10^-3之间;橄榄油与玉米油、猪油、牛油和鸭油的OPLS-DA鉴别模型准确性稍好,3个变量δ¹³C、δ²H和δ¹⁸O对不同油脂区分的贡献度VIP值分别为...     

Study on distribution pattern of stable carbon isotope ratio of Chinese honeys by isotope ratio mass spectrometry

The δ ¹³C values of 26 varieties of Chinese pure single‐flower honeys, 323 census samples of six varieties of single‐flower honeys and one multi‐flower honey as well as 20 888 commercial honey samples from 135 honey‐related enterprises in 25 provinces of China were analysed by stable carbon isotope ratio mass spectrometry between 1998 and 2004. It was found that the δ ¹³C values of different Chinese honeys fell within the ranges of values proposed by JW White. This shows that White's theory of the stable carbon isotope ratio of honeys is applicable to Chinese honeys and further demonstrates that the theory is universal to honeys from all over the world. The study also confirmed that the δ ¹³C values of honeys do not bear much relation to the environment in which the honey plants are grown, e.g. geographical area, water and soil, climate, etc., but do vary slightly with the honey plant species. Copyright © 2005 Society of Chemical Industry     

Assessing natural organic matter treatability using high performance size exclusion chromatography

This paper reports the use of high performance size exclusion chromatography (HPSEC) as a tool to assess NOM removal by coagulation. Quantitative information such as percentage removal can be determined after "peak-fitting" the HPSEC molecular weight profile of the source water. A peak-fitting approach was developed based on the molecular weight profile of dissolved organic matter from surface water. A sequential jar testing procedure with five treatment steps was used to characterize organics and to confirm that several NOM components were recalcitrant to coagulation with alum. Despite differences found in both the concentration and character of NOM in three surface waters studied, the final concentrations and characteristics (e.g., molecular weight profile) were very similar after five treatment stages. The molecular weight profiles of the recalcitrant organics were subsequently used to build a peak-fitting technique for NOM removal. The approach was validated by further jar test results of several other water sources, such as ground and river waters, including one found to be very difficult to treat in terms of NOM removal by alum treatment. Predictions of removable and nonremovable organic fractions by coagulation using this peak fitting technique were found to be within 10% of actual values.     

Alkylpyrazine contents of coffee beverages using stable isotope dilution gas chromatography–mass spectrometry

In the presented study the effects of key brewing parameters (temperature, holding time and storage conditions of coffee powder) on 12 alkylpyrazines in coffee beverages were investigated. The results show that the alkylpyrazine profiles of coffee beverages are similar to those of the coffee used. In total, 70–82% of the alkylpyrazines (113.3 ± 3.5 to 132.6 ± 0.6 mg/kg), depending on the brewing method, passed into beverages during the brewing process. At temperatures higher than 50 °C the alkylpyrazine contents of coffee beverages were almost independent of the brewing temperature. During a 30 min holding time at room temperature the alkylpyrazine contents of a freshly brewed cup of coffee decreased by about 10%. Furthermore, storing coffee in closed systems for up to 29 days at +4 °C, −20 °C or room temperature (+22 °C) had minor effects on the alkylpyrazine contents of beverages produced from the coffee. The results show that under customary conditions more than 70% of the alkylpyrazines present in ground coffee are transferred to beverages during the brewing process. Estimated total amounts of alkylpyrazines ingested by the consumer per cup of coffee beverage are in the milligram range, sufficient to have significant potential health effects.     

Gas chromatography carbon isotope ratio mass spectrometry applied to the detection of neutral alcohol in Scotch whisky: an internal reference approach

Ethanol and the volatile congeners of Scotch whisky have been analysed by GC–combustion stable isotope ratio mass spectrometry (GC–C–IRMS). Ethanol, propan-1-ol, 2-methylpropan-1-ol and methylbutan-1-ol (2- and 3-methylbutan-1-ol) have been separated using gas chromatography and their ratios of stable isotopes of carbon (¹³C/¹²C) determined by combustion isotope ratio mass spectrometry. The internal isotopic correlations for the ethanol and the congeners from the same sample were determined. A close and reproducible correlation was found for ¹³C/¹²C ratios of propan-1-ol and ethanol in authentic whisky samples and is the basis for determining the addition of neutral alcohol to whisky. Initial studies suggest that the method has the ability to detect the addition of neutral alcohol, depending on the cereal source of the whisky and neutral alcohol concerned, without the need for reference to databases.     

Authentication of tequila by gas chromatography and stable isotope ratio analyses

Gas chromatographic (GC) determination of volatile constituents and isotope ratio mass spectrometry (IRMS) analysis of ¹³C/¹²C isotope ratios as well as SNIF-NMR analysis of (D/H)-ratios of ethanol in authentic (n=12) and commercial tequila samples (n=13) were used to differentiate analytically between tequila derived from 100% agave (Agave tequilana Weber var. Azul) and tequila produced with other fermentable sugars ('mixed' tequila). Evaluating the correlation of methanol and 2-/3-methyl-1-butanol concentrations, GC analysis was found to be a suitable method for the authenticity assessment of '100% agave' and 'mixed' tequilas. Additional determinations of ¹³C_VPDB and (D/H) ratios of ethanol were used to show the perspectives and limits of the methods.     

Determining the geographic origin of milk in Australasia using multi-element stable isotope ratio analysis

A pilot study was conducted to evaluate the suitability of multi-element isotope ratio analysis for determining the origin of cows’ milk produced within Australasia. A milk sample from pasture-fed cows was obtained from seven dairying regions in Australia and New Zealand and analysed for the ratios of ¹³C/¹²C, ¹⁵N/¹⁴N, ¹⁸O/¹⁶O, ³⁴S/³²S, and ⁸⁷Sr/⁸⁶Sr. Each milk sample displayed a distinct isotopic fingerprint. Isotope ratios for ¹⁸O/¹⁶O and ¹³C/¹²C, in particular, conformed to predicted isotope fractionation patterns based on the latitude and climate of each region. Relative to skim milk, casein was enriched in ¹³C and ¹⁵N, and depleted of ³⁴S, whereas, predictably, ⁸⁷Sr/⁸⁶Sr ratios remained equivalent in both skim milk and casein. The milk samples from Australasia were considerably enriched in ¹⁸O and ³⁴S compared with reported values for most European dairy products. Overall, multi-element isotopic analysis has good potential for determining the geographic origin of dairy products produced within Australasia.     

Quantitative analysis of glycoconjugate precursors of guaiacol in smoke-affected grapes using liquid chromatography–tandem mass spectrometry based stable isotope dilution analysis

Guaiacol has been shown to accumulate in glycoconjugate forms in the fruit and leaves of grapevines following vineyard exposure to bushfire smoke. To investigate the glycosylation of guaiacol in smoke-affected grapes, a quantitative stable isotope dilution analysis method using liquid chromatography-tandem mass spectrometry was developed and validated, using the [²H₄]-labelled analogue of guaiacol β-d-glucopyranoside as internal standard. The method was subsequently applied to the analysis of grapes sampled from grapevines exposed to either bushfire or experimental smoke, enabling compositional comparisons of guaiacol glycoconjugates in smoke-affected grapes from different varieties to be determined, for the first time.     

Identification of geographical origins of Schisandra fruits in China based on stable carbon isotope ratio analysis

A method based on elemental analyser-isotope ratio mass spectrometer (EA-IRMS) was developed for the identification of the geographical origins of Schisandra fruits which are used as traditional Chinese medicines and important food materials. A total of 96 authentic samples from seven provinces in China were collected and subjected to stable carbon isotope ratio analysis (SCIRA), and the results showed that there were significant differences between the mean δ¹³C values of samples from different origins. By using single analyte δ¹³C, the Schisandra fruits from northeast China and south China could potentially be discriminated. A follow-up study will combine trace elements with stable isotope ratios to analyse a larger set of samples, to confirm the discrimination capability of ¹³C and to enhance the discrimination between close geographical regions.     

Enantioselective capillary gas chromatography and stable isotope ratio mass spectrometry in the authenticity control of flavors and essential oils

Abstract

Two phenomena, enantioselectivity and isotope discrimination, during biosynthesis may both serve as endogenetic parameters in the authenticity control of natural flavor and fragrance compounds, if suitable methods and comprehensive data from authentic sources are available. Enantioselective capillary gas chromatography (enan‐tio‐cGC) and comparative isotope ratio mass spectrometry (IRMS), coupled on‐line with cGC, are reported as important tools in the authenticity control of flavors and essential oils. The literature on these topics is reviewed up to the beginning of 1995. Scope and limitations of enantio‐cGC and (enantio)‐cGC‐IRMS are discussed.     

Compositional differences between size classes of dissolved organic matter from freshwater and seawater revealed by an HPLC-FTIR system

The molecular complexity of dissolved organic matter (DOM) hinders its characterization. New approaches are thus needed for a better understanding of DOM reactivity and fate in aquatic systems. In this study, high-performance liquid chromatography (HPLC), using size-exclusion separation, was coupled with Fourier transform infrared spectroscopy (FTIR). A solvent-elimination interface was used to deposit DOM fractions onto a germanium disk that were then analyzed by FTIR. Samples included ultrafiltered DOM (UDOM) and fulvic acids from the St. Lawrence Estuary and its tributaries. Results showed significant compositional changes with molecular size and origin, especially in UDOM. Larger fractions of UDOM contained more carbohydrates, amides, aromatics/alkenes and aliphatics, while smaller fractions contained more carboxylate and OH groups. Small marine molecules (500-900 Da) were also enriched in sulfate groups that appeared bound to UDOM. Large marine molecules were the most amide-rich fractions. Fulvic acids were enriched in carboxylate and OH groups, showed little changes in composition, and appeared similar to small terrigenous (riverine) UDOM even in marine water. This work shows that an HPLC-FTIR system is a powerful and complementary tool in the characterization of DOM. The compositional changes observed may explain the reported contrasting reactivity and fate of DOM having different size and origin.     

An isotope effect on the comparative quantification of flavonoids by means of methylation-based stable isotope dilution coupled with capillary liquid chromatography/mass spectrometry

Ionization suppression is a serious problem in liquid chromatography/mass spectrometry-based metabolomics, and stable isotope dilution-based comparative quantification is one of the most important methods of overcoming this problem. Herein, the use of [(13)C]-methylation-based stable isotope dilution for comparative quantification of flavonoids is demonstrated. This is in contrast to the equivalent deuterium labeling methylation method, which has an adverse isotope effect on reverse phase chromatography.     

Multielement stable isotope ratio analysis of glycerol to determine its origin in wine

 The adulteration of wine with glycerol is considered to be a problem in European wine-producing countries. The latest control methods are mainly based on the detection of impurities from commercial products, but suffer from the raising efficiency of the purification processes. As there is little chance of being able to identify glycerol from different sources on the basis of a method which uses only one isotope, a multielement approach was tested. Glycerol from wine showed the lowest relative enrichment with D, mainly in position C-2, a relatively high ¹⁸O content, and very negative δ¹³C values, which significantly correlated with those of ethanol from the same wines. The isotopic data of glycerol samples from different sources were in agreement with those given by indices of origin (impurities). These data allowed us to identify the origin of these glycerol samples, i.e. whether they were produced industrially or synthesised by animals or plants. Glycerol of plant origin was most similar to glycerol found in wine. The combination of several isotopic data by discriminance analysis yielded clusters of data obtained from glycerol samples of similar origin. Taking into account the characteristics of possible mixtures, proof that wine has been adulterated depends on the origin and isotope levels of the added compound. This study showed that it is possible to prove that wine has been adulterated with glycerol from other sources when the latter is present at a concentration of 15% of the total glycerol content. Received: 27 October 1997 / Revised version: 12 February 1998     

稳定同位素比值质谱法鉴别猪油中掺杂石蜡的研究初探

采用元素分析仪-稳定同位素比值质谱法开展了猪油中掺杂石蜡的鉴别技术研究。以猪油为掺杂对象和工业石蜡为添加物,分析测定了不同猪油样品和不同厂家的石蜡样品中δ~(13)C值大小,并对石蜡掺杂量与δ~(13)C值进行了相关性分析和回归分析。猪油中δ~(13)C值的分布范围为-21.089×10-3~-16.418×10~(-3),石蜡中δ~(13)C值分布范围为-32.128×10~(-3)~-30.713×10~(-3),两者存在明显差异。当石蜡添加量达到10%时,可鉴别出猪油中是否添加了石蜡,根据回归方程可对猪油中石蜡的含量进行初步估算。该方法简便快速,能为动物油脂掺假行为的监管提供技术参考。     

Development of a sensitive method for the determination of acrylamide in coffee using high-performance liquid chromatography coupled to a hybrid quadrupole Orbitrap mass spectrometer

The emerging trend towards high-resolution mass spectrometry (MS) alternatives was evaluated by the application of Orbitrap MS for the determination of acrylamide in coffee samples. The high resolving power of the Orbitrap MS provided the high selectivity and sensitivity that enabled quantitative analysis of acrylamide in complex matrices, such as coffee. Several sample preparation methods and scanning modes of the MS (full MS, t-SIM, t-MS2) were assessed in order to optimise parameters of the analytical method. The final procedure involved the extraction of acrylamide with acetonitrile, solid-phase extraction with dispersive primary secondary amine (PSA) and amino columns, and the detection by ultra-performance liquid chromatography coupled to a hybrid quadrupole-Orbitrap MS (HPLC-Q-Orbitrap) operated in targeted MS2 scanning mode. The repeatability of the method at the lowest calibration level (10 μg kg^?1), expressed as relative standard deviation, was 7.8% and the average recovery of acrylamide was 111%. The proposed method was applied to the determination of acrylamide in 22 samples of roasted coffee obtained from the Latvian retail market. Acrylamide concentration in coffee samples was in the range of 166–503 μg kg^?1.     

Comprehensive analysis of umami compounds by ion-pair liquid chromatography coupled to mass spectrometry

An ion-pair LC-ESI-MS method was developed capable of analyzing various reported umami or umami-enhancing compounds, including glutamic acid and 5'-ribonucleotides. The method was validated using tomato and potato samples and showed overall good analytical performance with respect to selectivity, detection limit, linearity, and repeatability. The method was applied to various tomato samples resulting in concentrations of glutamic acid and 5'-ribonucleotides that were in good comparison with literature. The methodology might also be used for the discovery of new umami (enhancing) compounds in an untargeted mode. This was to a certain extent demonstrated for tomato samples by correlating all peaks observed with the ion-pair liquid chromatography-mass spectrometry (LC-MS) method to sensory properties using multivariate statistics. PRACTICAL APPLICATION: This study describes the development and application of a LC-MS method, which can be used to quantify several known umami (enhancing) compounds in various foods. Furthermore, the method might be useful for the discovery of new umami (enhancing) compounds.     

基于稳定同位素比值的不同产地枸杞特征分析及判别

原产地差异导致枸杞价格悬殊,为促进国内枸杞市场健康有序发展,该文应用元素分析仪-稳定性同位素质谱（elemental analyzer-stable isotope mass spectrometry, EA-IRMS）测定了来自青海、宁夏和新疆3个地区共97份枸杞样品δ¹³C、δ¹⁵N、δ²H、δ¹⁸O和δ³⁴S 5种稳定同位素组成,结合箱线图、单因素方差分析以及主成分分析（principal component analysis, PCA）对不同产地枸杞中稳定同位素比值分布规律和相关性进行了讨论,应用线性判别分析（linear discriminant analysis, LDA）和支持向量机（support vector machine, SVM）2种算法建立不同产地枸杞判别模型。结果显示,枸杞样品中δ¹³C、δ¹⁵N、δ²H和δ¹⁸O 4种稳定同位素对产地判别贡献率较大,δ^...     

Model assessment of biogeochemical controls on dissolved organic carbon partitioning in an acid organic soil

A chemical model (constructed in the ORCHESTRA modeling framework) of an organic soil horizon was used to describe soil solution data (10 cm depth) and assess if seasonal variations in soil solution dissolved organic carbon (DOC) could be explained by purely abiotic (geochemical controls) mechanisms or whether factors related to biological activity are needed. The NICA-Donnan equation is used to describe the competitive binding of protons and cations and the charge on soil organic matter. Controls on organic matter solubility are surface charge and a parameter, gamma, that accounts for the distribution of humic molecules between hydrophobic and hydrophilic fractions. Calculations show that the variations in solute chemistry alone are not sufficient to account for the observed variations of DOC, but factors that alter gamma, such as biological activity, are. Assuming that DOC in organic soils is derived from soluble humic material and that gamma is modified seasonally due to biological activity (with monthly soil temperature used as a surrogate for biological activity) we are able to model the observed seasonality of soil solution DOC over a 10-year period. Furthermore, with modeled DOC coupled to other geochemical processes we also model soil solution pH and Al concentrations.     

Effect of dissolved organic carbon on sorption of pyrethroids to sediments

Despite their strong hydrophobicity, recent studies showed widespread occurrence of pyrethroid in downstream surface waters bodies. In this work, the effect of dissolved organic carbon (DOC) on the sorption and desorption of pyrethroids in sediment was evaluated to understand the role of DOC in facilitating pyrethroid transport. Presence of DOC from three sources at 38 ± 2 mg L?1 in the aqueous phase decreased pesticide sorption to a sediment by 1.7 to 38.9 times and increased their desorption by 1.2 to 41.4 times. The effect on pyrethroid sorption to the sediment was linear. In addition, interactions between DOC and pyrethroids, when taking place prior to the contact with sediment, decreased sorption of some pyrethroids even further, implying that DOC-pyrethroid complexs were relatively stable in solution. DOC sources with higher contents of carboxylic and phenolic groups were found to have a higher potential to associate with pyrethroids. The DOC-water partition coefficients (K(DOC)) obtained by solid-phase microextraction measurement were significantly correlated (P < 0.01) with K(d) values measured for the sediment. These results provide evidence that DOC increases the distribution of pyrethroids from the sediment to the solution phase and plays an important role in mobilizing pyrethroids in runoff and surface streams.